Variable-inductance coil



1,638,385 1927' 5. J. WOOD ET L VARIABLE INDUCTANCE COIL Filed NOV. 22. 1924 W I3 H- w I3 14 4. 'i

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INVEIYNRJ JM/VI'MD J W000 A GREENE JR.

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Patented Aug. 9, 1927.

:VARIABLE-INDUCTANCE dQIIQ.

Application fi led November 22, 1324 Serial No. 7,51,494.

,This invention relates vto a variable inductance device, and ,more particularly .to such a device adapted for use in radio ,i'requency circuits.

{In such inductances it ,is now, common to ,provide a stationary coil and a movahle coil, connected il series, and so arranged that theaxes of the two coils may be varied relatively to each other whereby theirmagnetic interlinkage may at.ivill he made to vary between the full. cumulative and ,the

full differentialcondition. The cumulative position corresponds ,to the maximum infductance setting, while the opposite .difi'eri5 ential position corresponds to the minimum inductance setting. Allthis is now Well understood, and is set forth herein to define I the typeofdevice to ivhiclrour invention/m lates. v r

It is one of the objectsof our invention to provide in general' an improved fprinof such variable inductances. i

It is still another object of our invention tohprovide a pluralit-y of variable inductances which may be operatechby the aid of a sin gle. movable member, such as a shaft,- and set relatively closely together Without ,danger oi the elements interfering, due to. their stray fields or the like.

In variable inductance coils of this gen- .cral character, it is highly desirahlethat 'lhe noven' ent of the movable coil relatively to the stationary coilbeproportional to the eilect of such n'iovementon. thecircuit in which the coil is placed. ,l orexan ple, in

a radio receiving system, when tuning to. re-

ceive signals from a station, the .tuning is usually produced by varying the resonance or the .wave length at which the receiving circuit is in tune. It is highly desirablethat' substantially equal increments of ave length variation be secured for equal increments of variation of the coil position.

In prior devices, the movable and stationary coils were arranged and ivere so constructed that this characteristic could not readily be obtained. One contributing rea .son fOlfllllllSdS that upon avariation in the relative positions "oi the two coils, thene is a corresponding variation in,the. distributed capacity betweenthe coil layers. lt is pos sible to secure ,amore uniform calihration by insuring that the distributed capacity ,stays. constant, or substantiallyso, for any setting ofthe two coils. Itisthusanother object of our invention-to, ensure that the distributed capacity of the variable ,inductance stays substantially. constant vithin the range of operation .of the nstrument.

,Qur invention possesses other advantageous features,son1e of Which withitheforegoing, ,Will be set forth ,at length. in the following description, vhe re veshall outline in full that form of t reinvention which We have chosen for illustration in the drawings accompanying an.cl torining part of the' present .specifica'tionf Although We have shown in the drawings but. one ffornrot our ,inven. tion..,\ve do not desire {to bellimitedthereto, sincethe invention defined in the; claims maybe embodied in other fornis also.

Referring .to ,the drawings:

Figure 1 is a side view showiug an installation ,utilizing a pair of ,variable inductances built in. accordance vith our .invention one of the inductaneesbeing insection; I

r .Fig. 2 is a perspectivevieiv of one q'fi t he coil elements utilized in our, invention I an d Figs. 3 and 4c are diagrammatic vic vs, illustrating how the positions of the coils may ;be variedto vary the eil'ective iuduc- .tan'ce ofv the, entire device.

Tllhe "stationary coil element of, our ,devicecomprises, one or more coil sections 11' which are arranged ina circle, as shown diagram-. matically in Figs. 3 and The ,magnetic aigis of ,thesecoils. is, indicated the arrow 12in-Figs .fi-land .4,.and is seen tobe radial .ii ith res pectiothe circle formed by the two coils 11. The actualconstructionof tlie coils l nayfl best appreciated by [an inspection of 2,. in. vwhich Ave have shown the coils .Jl asmade up of asinglclaycr of turns. v,It is seen that the long .sides ot the coils l1 are arcu ate. in shapc, SO asto lit withinthe ,hollow,tubular, support 13 as shown inE ,1. flhissupportfl is stationary and is held as theaid of one or more brackets 14 to a stationarypanel 10. Q'Lhe coils 11 may be held to the'inn er surface of lhetuhular support lfi hytheaid ofappropri t fastening devices ,or by glue, collodion, or the like.

The, tubular-support 13 in this instance has an end ,Witll. l5, which supports, a central ,hub 16, serving asl a beariin support ton tlie main operating shaft 17. ,In Fig.1, e illustrate a pair ot stationary supports 13, .throughwhich,thesh aft 17 e 'tends; but it is to be understood that. any number of such supports, eachcorrespondingmai be alin ed as. require; fori the f particular installation.

the arrow in Fig. 4.

The movable coil element is formed of two coils 18 located in this instance within the circle formed by the coils 11, and rotatable with respect thereto. These coils also extend angularly for a sufficient distance to form substantially a complete circle, each extending about 180 and have magnetic axes which are coplanar with the axis 12 of the stationary coils 11. The axis for the coils 18 is indicated b the arrow 19 in Fig. 3, and The magnetic axes of all the coils are not only coplanar, but fall substantially along radii of the tubular support 13.

The coils 18 are given revolutionary movement by the rotation of shaft l't', which has an axis coaxial with that of the tubular support 13. For this purpose there is mounted on the shaft 17a rotatable support 21, which has a tubular portion 22. On the outer cylindrical surface of this portion 22 are fastened the coils 18. The support 21 is held on the shaft 17 by the aid of any appropriate means, such as the set screw as passin through a hub 23 formed integrally with tile support 21. V

The coils 11 and 18 are all connected in series in any circuitthat is to be tuned. By rotating shaft 17, it is possible to vary the relative position of the axes of the two sets of coils 11 and 18. In this way, the coils may be changed from full cumulative position to full differential position by a rotation through 180 degrees. Thus in Fig. 4 the full differential position is indicated. The arrow 12 indicates the axis and amount of the magnetic field set up by the coils 11; while the arrow 20 shows the equal and opposite effect of the movable coils 18. These two values substantially neutralize each other, and the device is then in the minimum inductance position. By rotating the shaft 17 in a clockwise direction, the full differential position is departed from and the total inductance of the device gradually increases. Thus for the intermediate position illustrated in Fig. 3, the axes of the two sets of coils are illustrated by the arrows 12 and 19, which are at right angles to each other. In this position the vector sum of these two arrows represents the effective inductance of the device. By continuing the rotation of shaft 17, the coils will fall in a position which is similar to that illustrated in Fig 4, except that the two arrows 12 and 20 would be drawn in the same direction and not in'the opposite direction. This is the full cumulative position, and corresponds to the maximum inductance obtainable by the use of our device.

Several features of the construction of the device may now be emphasized more particularly. One feature which is of great importance, resides in the fact that the coils 11 have a field which is limited to a substantially narrow band extending around the axis of shaft 17. It is for this reason that it is possible to mount two variable inducthe axes of all of the coils, with respect to the axis of shaft 17. The net result is that the resultant ma netic field of any one set of coils, is confined to a narrow band around the axis of shaft 17 It is further to be noted that coils 11 and 18 have an angular extension sufficient to s3 form substantially a complete circle or ring. Due to this feature, the distributed ca acity which exists between the two layers of coils, remains substantially constant independent of the relative positions of the coils. This .1 distributed capacity is produced by the juxtaposition of one set of conductors making up the coils 11, with respect to the other set atjacent thereto making up the coils 18. The calibration of the instrument is found a.) to be more uniform, since it is found thatequal angular movement of shaft 17 produces equal increment in the wave length to which the circuit is to be tuned.

Since we are able to utilize two or more can such devices on a common shaft 17 without interference, it is quite feasible to tune a plurality of circuits simultaneously by the operation of a single shaft such as 17. Such a feature is of considerable importance 1 5 where a plurality of tuned radio circuits are used, as for example in tuned radio frequency amplifier stages in radio receiving systems. Of course, other applications may also be found for our invention.

It is also evident that the particular shape of the coils 11 and 18 may be materially departed from, while yet maintaining some of the advantages of our invention.

. We claim:

1. In combination, a pair of relatively movable coils, each of said coils being of loop form, two opposite sides of the loop corresponding to the periphery of a surface of revolution, these sides extendin over a large angle of said surface, and displaced. from each other along the axis of the surface so that the coils extend only a short axial distance as compared with the angular extent of the coil, the coils of the pair being placed on parallel surfaces of revolutioif so as to affect each other, and means for supporting the coils so that the coil axes form radii of the said surfaces of revolution.

2. In combination, a plurality of stationary coils, said coils being of loop form, two opposite sides of each coil corresponding substantially to the periphery of a surface of revolution, these sides being displaced from each other along the axis of said surface, the coils being angularly displaced in such manner that the combined angular extent of these sides extends substantially completely around the said periphery, the other opposite sides of the loops being short whereby they occupy a narrow space only along the axis of the surface of revolution, a plurality of cooperating movable coils similarly ar, ranged to the stationary coils and'also having sides the combined angular extent of which extends substantiall 1 around a similar periphery parallel to the other periphery,

the stationary and movable coils having axes rad1al to said surfaces, and means for mow ing the movable coils so to vary the relative angular positions of the axes of the coils, whereby the extent of adjacent surfaces of the stationary and movable coils remains substantially unaltered during the said movement.

3. In combination, a plurality of pairs of relatively movable coils, each of said coils being of loop form, two opposite sides of the loop corresponding to the periphery of a surface of revolution, these sides extending over a large angle of said surface, and displaced from each other along the axis of the surface so that the coils extend only a short axial distance as compared with the angular extent of the coil, the coils of each pair being maintained on parallel surfaces of revolution, so as to affect each other, and the plurality of pairs being displaced from each other in a direction along the common axis of the said surfaces, and means for simul-' taneously varying the relative angular positions of the coils in each pair.

4-. In combination, a pairof stationary coils, said coils being of loop form, two opposite sides of each coil coresponding substantially to the periphery of a surface of revolution, these sides being displaced from each other along the axis of said surface, and each extending substantially 180 along the periphery, and said pair of coils forming in combination a substantially complete ring along said periphery, the other opposite sides of the loops being short whereby they occupy 1 a narrow space only along the axis of the surface of revolution, a pair of cooperating movable coils similarly arranged to the sta tionary coils and each also having sides extending substantially 180 along a periphery similar and parallel to the other periphery, and both movable coils forming a substantially complete ring, the stationary and movable coils-having axes radial to said peripheries,-and means for moving the movable coils so as to vary the relative angular positions of the axes of the coils, whereby the extent of the adjacent surfaces of the stationary and movable coils remains unaltered during said movement.

5. In combination, a plurality of pairs of stationary coils, said coils being of loop form, two opposite sides of each coil corresponding substantially to the periphery of asurface of revolution, these sides being dis placed from each other along the axis of said surface, the coils of each pair being of equal angular extent and singularly displaced in such manner that the combined angular extent of these sides extends substantially completely around the said periphery, the other opposite sides of the loops being short whereby they occupy a comparatively narrow space only along the axis of said surface of revolution, a plurality of pairs of mov-- able coils similarly arranged to the stat1onary coils and each pair also having sides the combined angular extent of which extends substantially completely around a similar periphery parallel to the other periphery, these stationary pairs of coils and movable pairs of coils being arranged to cooperate with each other so that a pair of stationary coils cooperates with a pair of movable coils to form a unit, the plurality of units thus formed being displaced from each other along the common axis of the said surfaces,

means for moving the movable coils simnl-- taneously so as to Vary the relative angular positions of the axes of the coils in each unit, whereby the extent of adjacent surfaces remains substantially unaltered during said movement, and whereby the electrical field of the coils in each unit remains in a comparatively short space along the axis of revolution. In testimony whereof, we have hereunto set our hands.

STANFORD J. lVOODQ HARRY A. GREENE, JR. 

